The communist-leaning Naxalites guerrillas, who say they are inspired by Chinese leader Mao Zedong, have been fighting for more than three decades in several Indian states. (File photo, 2010)

Indian police officers raided a Maoist-Naxalite gathering in the eastern state of Odisha, killing 24 rebels in a "shoot-out," police officials said on Monday.

The Maoists, better known as Naxalites, have been at war with India for decades in what they call a semi-feudal state, accusing the country of neglecting land and job rights of tenant farmers and the poor. Government data shows nearly 8,000 people have been killed between 2001 and 2012 in the deadly conflict.

Police were tipped-off that around 30 rebels had gathered close to the border with Andhra Pradesh state, Odisha police chief KB Singh said.

"Immediately after seeing the police forces, the Maoists began firing at them and the police had to retaliate," N Sambasiva Rao, the Andhra Pradesh director general of police said, according to local sources.

Local media also said two police officers were injured in the battle.

Where do the Naxalites operate?

India's Maoist insurgency began in the state of West Bengal in the 1960s, triggering what former prime minister Manmohan Singh called the group India's most serious internal security threat. The rebels operate in at least 20 Indian states but are most active in the forested and resource-rich areas of Chhattisgarh, Odisha, Bihar, Jharkhand and Maharashtra.

They draw recruits from tribal communities whose members are often desperately poor and living in underdeveloped areas neglected by successive governments.

The level of violence has fallen in recent years as the Maoists have lost hundreds of fighters to desertions and battles with security forces. However, the rebels remain capable of staging regular hit-and-run attacks, a tactic seen across several Indian states.